LizardRunner
04-21-2011, 11:01 AM
As Jeep XJ owners, we all get to read millions of words about overheating. It seems that if you own an XJ, you will at some point experience this bugger of a problem. Like wise there seems to be millions of ways to fix the problem, so many in fact that while reading these wise words one can become frusterated and befuddled enough to just give up.
These issues with overheating seem to mostly stem from missinformation or a lack of true understanding of cooling systems, which led me to do this write up so everyone could have some knowledge of how to approach a cooling system snafu when it occurs.
The first thing I am always amazed about is how most people tend to think cooling systems are simple. The truth is, the physics that go into proper design is complex. Each independent part is relatively simple but when married together into a complete system, often times it becomes a matter of not working together well that causes the problems. Everyone knows there is a radiator, hoses, thermostat, overflow bottle but most forget that the heater is also part of this system on a "street" vehicle. Add the misconceptions of distilled water Vrs. the 50/50 mix touted by antifreeze makers. The need for pressure to prevent boil over, the importance of a high flow rate pump and the inter-relationship of system performance and the thermostat. You can see how it would make the head swim in circles.
The function is well known, water/coolant removes heat from the engine. How much heat to remove is critical, to much cooling and the engine doesn't perform well, to little cooling and things begin to weld together, either is not good. Pressure allows the coolant to perform with out boiling over to quickly. How much pressure determines how much heat the engine retains, which is dependant on what temperature is optimal for the engine. Our XJ's apparently like to operate at 200-210 F, so this is where we want to always see the temp needle on the gauge. Radiators remove heat from the water/coolant, which removes heat from the engine block, heads and cylinders. It is not wise to run any system without the thermostat, the thermostat and the radiator cap are the pressure regulators, which as stated above, keep the pressure high enough to keep the water/coolant from boiling at to low a temperature.
The order I trouble shoot a coolant problem is: lower radiator hose, upper radiator hose, thermostat, water pump, heater hoses and core, water galleys, fans. Naturally you don't have to go in any order unless you don't know where the problem might be. I just find this order to be the fastest route on an unknown vehicle.
Fans by the way are huge use the wrong one/s and you can create bigger problems. Pullers (behind the radiator) are far better than pushers (in front of the radiator). Shrouds should be as deep (extended behind the blades) as possible. This ensures as much air flow through the radiator as possible. Electric fans do not suck horse power from your engine, the good old belt driven clutch fan will suck about 10 hp from your total hp. Distilled water holds more heat than a 50/50 mix of water and antifreeze. Antifreeze is used to raise the boiling point not to actually remove more engine heat.
Rather than fill three pages I will refer those interested in further information to: This article by billavista http://pirate4x4.com/tech/billavista/Cooling/
These issues with overheating seem to mostly stem from missinformation or a lack of true understanding of cooling systems, which led me to do this write up so everyone could have some knowledge of how to approach a cooling system snafu when it occurs.
The first thing I am always amazed about is how most people tend to think cooling systems are simple. The truth is, the physics that go into proper design is complex. Each independent part is relatively simple but when married together into a complete system, often times it becomes a matter of not working together well that causes the problems. Everyone knows there is a radiator, hoses, thermostat, overflow bottle but most forget that the heater is also part of this system on a "street" vehicle. Add the misconceptions of distilled water Vrs. the 50/50 mix touted by antifreeze makers. The need for pressure to prevent boil over, the importance of a high flow rate pump and the inter-relationship of system performance and the thermostat. You can see how it would make the head swim in circles.
The function is well known, water/coolant removes heat from the engine. How much heat to remove is critical, to much cooling and the engine doesn't perform well, to little cooling and things begin to weld together, either is not good. Pressure allows the coolant to perform with out boiling over to quickly. How much pressure determines how much heat the engine retains, which is dependant on what temperature is optimal for the engine. Our XJ's apparently like to operate at 200-210 F, so this is where we want to always see the temp needle on the gauge. Radiators remove heat from the water/coolant, which removes heat from the engine block, heads and cylinders. It is not wise to run any system without the thermostat, the thermostat and the radiator cap are the pressure regulators, which as stated above, keep the pressure high enough to keep the water/coolant from boiling at to low a temperature.
The order I trouble shoot a coolant problem is: lower radiator hose, upper radiator hose, thermostat, water pump, heater hoses and core, water galleys, fans. Naturally you don't have to go in any order unless you don't know where the problem might be. I just find this order to be the fastest route on an unknown vehicle.
Fans by the way are huge use the wrong one/s and you can create bigger problems. Pullers (behind the radiator) are far better than pushers (in front of the radiator). Shrouds should be as deep (extended behind the blades) as possible. This ensures as much air flow through the radiator as possible. Electric fans do not suck horse power from your engine, the good old belt driven clutch fan will suck about 10 hp from your total hp. Distilled water holds more heat than a 50/50 mix of water and antifreeze. Antifreeze is used to raise the boiling point not to actually remove more engine heat.
Rather than fill three pages I will refer those interested in further information to: This article by billavista http://pirate4x4.com/tech/billavista/Cooling/